Mechanism for generating variable electromotive force.



Patented Aug. 20, I90I. J. E. MILLER. MECHANISM FOR GENERATING VARIABLEELECTROMUTIVE FORCE. (Application filed Mar. 1, 1900.) (No Model.)

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i3 I M we I 8 WITNESSES: mvavmp @zw/ By ZTTOIM'EY.

JAMES EDGAR MILLER, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR TO THEWESTINGHOUSE ELECTRIC dc MANUFACTURING COMPANY, OF

PENNSYLVANIA.

MECHANISM FOR GENERATING VARIABLE ELECTROMOTIVE FORCE.

SPEGIFIGATION formiug' part of Letters Patent No. 680,798, dated August20, 1901.

Application filed March 1, 1900.

To all whom it may concern.-

Be it known that I, JAMES EDGAR MILLER, a citizen of the United Statesof America, residing at Edgewood Park, in the county of Allegheny andState of Pennsylvania, have invented an Improvement in Mechanism forGenerating Variable Electromotive Force, of which the following is aspecification.

My invention relates to the generation of IO electrical energy; and ithas for its object to provide a simple and efiicient means forgenerating electrical energy the electrornotive force of which may bevaried within wide limits.

With this end in View I have devised the mechanism shown in theaccompanying draw-- ings, in which Figure 1 is a diagram of apparatusand circuits suitable for practicing my invention. Fig. 2 is a viewsimilar to Fig. 1, but embodying a modified construction; and Fig. 3 isa view similar to Figs. 1 and 2, but showing a further modification.

It sometimes becomes necessary or desirable to supply electrical energyto translating devices at a variable potential when the only source ofenergy conveniently available supplies a constant or approximatelyconstant electromotive force. A familiar example is found in thecharging of secondary batteries from a constant-potential electric lighting or power circuit, it being necessary in the charging of batteriesto raise the potential of the charging-circuit as the charging operationproceeds, the ultimate potential, provided the batteries are charged tosubstantially their full capacity, being very much higher than thatrequired when the batteries are approximately free of charge. In orderto meet the requirements of such conditions, I propose to employsubstantially the means which will now be described, reference beingfirst had to Fig. 1 of the drawings, in which the armature 1 of adirect-current 1notor.2 is mechanically connected to the armature 3 of asimilar generator 4. This connection be tween the armatures of thegenerator and motor may be by means of belts and pulleys or other formof gearing, or the connection Serial No. 7,007. (No model.)

may be made direct by mounting the two armatures on a single shaft 5, asindicated, or by coupling the shafts together either rigidly or by aflexible coupling in a manner well known in the art. The armature 1 ofthe motor 2 is supplied with energy from a suitable source ofapproximately constant electromotive force through conductors 6 and 7,which may .represent the bus-bars of a switchboard, the usualstarting-box 8, and a commutator 9. The generator 4 supplies energy toconductors 6 and 7 which may be switchboard bus-bars or otherconductors, to which the translating devices to receive the energy fromthe said generator are connected. The connection between thegenerator-armature 3 and the conductors 6 and 7 is made by means of acommutator 10 in the usual manner. The field-magnet of the motor 2 isprovided with a shunt-winding 11, one terminal of which is connected tothe positive brush of the commutator 9 and the other terminal of whichis connected to one terminal of a variable resistance 12 of a rheostat12. The other terminal of the resistance 12 is connected to one terminalof the shunt field-magnet Winding 13 of the generator 4, the otherterminal of said winding being connected to the positive brush of thecommutator 10 and. to the conductor 6 The switch-arm 14: of the rheostat12 is connected with the nega 8o tive brush of the commutator 9 of themotor 2 by means of conductors 15 and 16 and with the negative brush ofthe commutator 10 of the generator 4 by means of conductors 15 and 17.The rheostat switch-arm let is movable over the stationarycontact-terminals 18 of the rheostat, and by reason of the connectionsof the resistance-terminals with the terminals of the field-magnetwindings 11 and 13 the entire resistance of the rheostat may 0 beincluded in circuit with one of the fieldmagnet windings, or any desiredamount may be included in circuit with one of such windings, and theremainder will necessarily be included in circuit with the otherfield-mag- 5 net winding.

The arrangement of apparatusshown provides two means which cooperate tovary the electromotive force supplied to the conductors (3 and 7 sincethe adjustment of the rheostat so as to increase the resistance of thecircuit including the winding 11 will result in an increased speed ofthe motor-armature 1, which will increase the electromotive forcesupplied by the generator 4, and the adjustment of the rheostat toincrease the resistance of the winding 11 will efiect a correspondingdecrease of the resistance of the circuitof winding 13, and consequentlyinsure an increase of exciting-current through the winding 13, whichwill raise the electromotive force of the generator. It follows,therefore, that if the apparatus is properly designed a maximumadjustmentof the rheostat will insure an extremely wide range in theelectromotive force supplied by the generator 4.

In Fig. 2 of the drawings I have shown my invention as practiced bymeans of a generator and a motor the field-magnets of which areseparately excited. The apparatus and circuits shown in Fig. 2 are thesame as those shown in Fig. 1, except in so far as modifications arenecessary in order to effect the separate excitation above mentioned,and the description given in connection with Fig. 1 may be read inconnection with Fig. 2, except as regards the features to be nowspecifically described.

The field-magnet winding 11 of the motor 2 is supplied withexciting-current from a small generator 19, a greater or less amount ofthe rheostat resistance 12 being connected in circuit with said windingand the armature of said exciter through the switch-arm 14, one of thecontact-terminals 18, and the conductors 15 and 16". The field-magnetwinding 13 of the generator 4 is similarly supplied withenergizing-current by the exciter 20, the circuit of said field-magnetwinding and exciterarmature being completed through more or less of therheostat resistance 12 by means of the switch-arm 14, contact-terminals18, and conductors 15 and 17. The field-magnet windings 21 and 22 forthe respective exciters 19 and 20 are connected in series across theconstant-potential conductors 6 and 7.

It will be readily seen without further description that the weakeningof the field of the motor 2 by adjusting the switch-arm 14 of therheostat to increase the amount of resistance in the winding 11 willresult in a speeding up of the motor, and consequently of the generator4 driven thereby, that such weakening of the field of the motor will beaccompanied by a corresponding strengthening of the field of thegenerator, and that the increased speed of the generator and theincreased strength of its field will cooperate to raise theelectromotive force supplied by it to the conductors 6 and 7, and thusinsure as wide variations of electromotive force as may be desired. Thereverse operatiomwhereby the generator electromotive force is decreased,is obvious.

In Fig. 3 of the drawings is shown a further modification, in which themotor 2 and the generator 4 have shun t-Wound field-magnets, thearrangement of circuits being, however, somewhat different from thoseshown in Fig. 1. Many of the parts are the same as have already beendescribed in detail in connection with Fig. 1, and the descriptionheretofore given may therefore be read in connection with Fig. 3, theonly additional description necessary being with relation to added ormodified features. In this form of my invention the adjacent terminalsof the field-magnet windings 11 and 13 are respectively connected to theends of the rheostat resistance 12, and the positive terminals areconnected to the conductor 7,they being shown as joined together at thepoint X, from which a single conductor leads to the conductor 7, thoughobviously the specific arrangement of conductors shown is not essential.The rheostat switch-arm 14 is connected by means of conductor 23 to themain conductor 6. It will be readily understood that the operation ofthis apparatus is in all essential particulars like that of each of theforms of my invention already described.

In case it is desired to employsubstantially the arrangement of circuitsshown in Fig. 3, but to separately excite the field-magnets of themachines 2 and 4" instead of making them self-exciting, I may employ asmall exciter 24 and connect it by means of the conductors indicated inthe broken lines to the circuits of the field-magnet windings l1 and 13at the points X and Y. In such case the conductors between the points Xand Y and the corresponding main conductors 7 and (3 would obviously beomitted.

In each of the modifications herein shown and described theenergizing-currents for the field-magnets of the generator and motorflow through the switch-arm of the rheostat in the same direction, andconsequently such currents flow in opposite directions in thecomplementary portions of the resistance 12.

WVhile I have illustrated and described certain apparatus andcombinations and arrangements of circuits, I desire it to be understoodthat my invention is not necessarily limited to What is specificallyillustrated in the drawings and described in the specification, the onlylimitations intended being those specified in the claims.

I claim as my invention- 1. Means for producing avariable electromotiveforce comprising an electric motor driven from an approximatelyconstant-potential circuit, a generator mechanically connected to anddriven by said motor, and means for increasing the field-magnet strengthof the generator and decreasing that of the motor simultaneously, andvice versa.

2. The combination with a direct-current motor having its armatureconnected to a source of approximately constant potential, of agenerator having its armature mecham ically connected to that of themotor, and means for inversely varying the resistance of thefield-magnet circuits of said machines.

3. The combination with a generator and a motor having their armaturesmechanically connected together, of means for supplying themotor-armature with energy at an approximately constant potential, avariable resistance connected in circuit with the fieldo. Thecombination with two armatures mechanically connected together one ofwhich receives and the other of which generates electrical energy, ofseparate field-magnets for said armatures the windings of which areconnected in series through a resistance, and a bridge across saidcircuit embodying a switch-arm for transferring more or less of saidresistance from one field-magnet circuit to the other.

6. The combination with two armatures mechanically connected togetherone of which is operated by electrical energy and the other of whichgenerates such energy, of separate field magnets for said armatureshaving windings connected in series through a resistance, and a bridgeacross the circuit of said windings comprising a switch-arm forprogressively transferring said resistance from one field-magnet circuitto the other.

In testimony whereof I have hereunto subscribed my name this 28th day ofFebruary, 1900.

J. EDGAR MILLER.

lVit-nesses:

WESLEY G. CARR, W. SUMNER SEIBERT.

